The invention relates to knock detection circuitry for a two cycle internal combustion engine.
Premature firing of the fuel-air mixture in the combustion chamber of an internal combustion engine causes the mixture to explode rather than burn smoothly. This phenomena is called knock or detonation, and results in loss of power and possible engine damage. Knock becomes more severe with lower fuel octane rating.
It is known in the art to sense knock with an audio transducer mounted to the engine, and to reduce knock by supplying a richer fuel-air mixture and/or adjusting spark timing, U.S. Pat. Nos. 4,243,009 and 4,667,637, incorporated herein by reference.
The present invention provides further improvements in the knock detection circuitry. Gated automatic gain control is provided for the knock transducer output voltage to vary same inversely with sensed background noise. Prior systems require a precise output from the knock transducer, and have a small tolerance deviation range. This in turn required precision transducers, and precision connection to the engine, including an exact torque specification. The present invention eliminates these precision requirements and self-adapts to varying knock transducer sensitivities.